Compared with 2G/3G networks, a Long Term Evolution (LTE) network only has a Packet Switched (PS) domain, and has no Circuit Switched (CS) domain. In the LTE network, a Voice over LTE (VoLTE) based on an IP Multimedia Subsystem (IMS) is a solution to realize voice service. The VoLTE can cooperate with the LTE network or a 4G Evolution Packet Core (EPC) network to realize an end-to-end voice service based on the PS domain.
To call a terminal, a base station may send a paging message to the terminal. The paging message carries a core network domain (Cn-Domain) name field. The Cn-Domain name field may have a value of PS or CS. That is, when the voice call is performed with VoLTE, the Cn-Domain name field has a value of PS, and when the voice call is performed with 2G/3G based on the traditional circuit domain, the Cn-Domain name field has a value of CS.